This invention relates to microscopes able to display a physical property of a surface and, more particularly, to a scanning probe microscope wherein a probe tip is moved over the surface of a sample in a raster scan comprising a series of transverse scans during which data reflecting the height of the surface is gathered at a plurality of data points to be used by controlling and calculating computer means to construct an image of the topography of the surface to scanning apparatus for increasing the speed of the scan comprising jump scanning means for moving the probe tip along each of the transverse scans in a series of jumps wherein the probe tip is moved from a position adjacent the surface to a height above the surface where there is virtually no possibility that the probe tip will strike the surface when the probe tip is moved horizontally and data gathering logic means included within the computer means for gathering the data at a pre-selected portion of selected ones of the jumps.
Scanning probe microscopes are rapidly gaining popularity because of their ability to display surface features to an atomic level with what are, compared to other microscopes of such capability, simple and inexpensive devices. Typical of scanning probe microscopes are the Scanning Tunneling Microscope (STM) as described in U.S. Pat. No. 4,343,993 by Binnig and Rohrer and the Atomic Force Microscope (AFM) as described in U.S. Pat. No. 4,724,318 by Binnig et al.
In the STM, a sharp metallic tip is maintained a few atomic diameters above the surface of a conducting surface while a tunneling current flows between the tip and the surface as the tip is scanned across the surface. As stated in the independent claim of above-referenced U.S. Pat. No. 4,343,993, the tip is scanned "across the sample surface at a tunneling distance while tunneling current flows between the tip and the sample surface." Since the tunneling current flows only when the tip is within a few atomic diameters of the surface, the STM has the advantage of seeing atomic features on the surface; however, the disadvantage is that on large scans where atomic resolution is of no interest, the tip must still be a few atoms above the surface. This makes it difficult to perform large scans at a fast scanning speed since the vertical positioning system cannot respond fast enough to keep the tip from hitting the surface, causing the tip to be worn away and also damaging the surface. For example, at the present time the fastest scan velocity for an STM is 10 microns/second over a "rough" surface such as a stamper for making compact disks. At higher velocities the tip tends to be damaged. This scan rate is about 20,000 atoms per second and the feedback response is about 20 kHz. The feedback system corrects the vertical position of the tip for a horizontal motion of one atom, which is the rate required to keep the tip from running into ledges which are more than a few atoms high. Faster responding positioners and feedback loops would be needed for faster scans. On large scans, such as a 25 micron scan with 200 data points per scan, nearly 500 corrections are made to the vertical position of the tip to keep it from hitting the surface between data points of the scan. In other words, it can be appreciated that most of the scan time is not involved with obtaining the data of the height of the surface; but rather, with just getting from one data point to the next without hitting the surface. Again, the reason is that the feedback systems employed rely on a tunneling current to flow continuously in order to servo the tip above the surface; but, the tunneling occurs only when the tip is a few atoms above the surface.
As mentioned above, an Atomic Force Microscope (AFM) is another type of scanning probe microscope. This device has a sharp tip mounted on a lever and the tip is brought down into near contact, or contact, with the surface of the sample to be scanned. The force of contact is measured by the deflection of the lever, usually by a beam of light which is bounced off the lever. With a feedback system moving the tip (or, alternatively, the sample) up and down to maintain constant force, the tip is scanned across the sample. If the force is kept small, the tip will not be damaged; but, on large scans the feedback system cannot respond fast enough to keep the force small, so the scan rate becomes limited in order to not damage the tip.
Wherefore, it is an object of this invention to provide a scanning probe microscope which can scan rapidly and accurately without fear of damaging the scanning probe or the sample.
It is another object of this invention to provide a scanning probe microscope which can scan rapidly and accurately without fear of damaging the scanning probe or the sample by scanning the probe over the surface of the sample in a series of hops or jumps rather than dragging the probe tip over the surface.
Other objects and benefits of the invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.